Torque transmitter

ABSTRACT

A torque transmitter includes three coaxial helically wound springs of different inner and outer diameters positioned relative to each other such that the inner and outer generally circumferential surface of the center spring form interference fits with, respectively, the outer generally circumferential surface of the inner spring and the inner generally circumferential surface of the outer spring. The inner and outer springs are wrapped in one direction and the center spring is wrapped in the opposite direction.

This is a continuation of co-pending application Ser. No. 07/318,628filed on Mar. 2, 1989, now abandoned.

FIELD OF INVENTION

This invention relates to torque transmitters and, more particularly, tohollow, flexible, small diameter devices for use in medicalapplications.

BACKGROUND OF INVENTION

There are in the art a number of flexible guide wires used in medicalapplications such as introducing catheters into human cardiovascularsystems. Exemplary such devices are shown in U.S. Pat. Nos. 3,789,841,4,538,622 and 4,545,390, which are hereby incorporated by reference. Asdiscussed in these prior patents, in one typical application, such guidewires are introduced into a patient's femoral or brachial artery and areadvanced through the artery into the coronary region, and the guide wireis manipulated to steer the device selectively into deeper and smallercoronary arteries. These prior art devices have a number of limitations.The wires tend to "set" when curved into the tortuous configurationrequired to follow along the artery and, particularly when curved, willnot transmit torque/rotation from end-to-end on a substantiallyone-to-one basis.

The art also teaches a number of flexible power transmission shafts andcouplings. See, e.g., U.S. Pat. Nos. 177,490, 779,374, 1,481,078,1,678,335, 2,573,361, 3,628,352, 4,112,708, and U.S. Pat. No. Re.25,543. These devices are, because among other things of their size, notuseful in medical cardiovascular devices. Moreover, their design andconstruction is typically such that substantially one-to-one rotationaltorque transmission is neither necessary nor desired. In the flexiblecoupling of U.S. Pat. No. Re. 25,543, the circumference and innersurfaces of the individual springs are either ground to size orotherwise calibrated in order to telescope the individual layers intoeach other with a tight fit.

SUMMARY OF INVENTION

The present invention provides a small diameter device that hassubstantially the same one-to-one rotational torque transmissioncharacteristics as a solid rod not only when straight but also when in ahighly tortuous configuration, and that also is hollow so that a wire orthe like can be fed through it.

The invention features a torque transmission device comprising threehelically wound wire layers. The inner and outer layer are wrapped inthe opposite helical directions from the central layer, and there is aninterference fit between the inner and outer circumferential surfaces ofthe center layer and, respectively, the inner and outer layers when notorque is being applied to the device, i.e., the individual springs areconstructed such that, standing alone and relaxed, the inner diameter ofthe central spring is less than the outer diameter of the inner springand the outer diameter of the central spring is greater than the innerdiameter of the outer spring. In preferred embodiments each layercomprises helically wrapped flat wire, and the inner and outer diametersof adjacent layers are such that, as compared to their non-overlappingstate, there is a radial interference of not less than about 0.001 inch.

In addition to being able to transmit rotation/torque (either clockwiseor counterclockwise) on an essentially one-to-one basis, the torquetransmitter of the present invention has numerous other advantages. Itis able to undergo tortuous bendings without kinking or setting, isresistant to longitudinal stretching and penetration, has high torsionalstiffness, and is easily made watertight.

DRAWINGS

FIG. 1 shows, partially cut-away, a torque transmitter of the presentinvention in which each layer is single strand wire.

FIG. 2 shows, partially cut-away, a torque transmitter in which eachlayer is multi-strand.

FIG. 3 schematically compares the torque transmitting characteristics ofthe present invention with those of a rigid rod.

FIG. 4 shows in longitudinal section a medical guide wire assemblyincluding the torque transmitter of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1 which disclose a torque transmitter,generally designated 10, embodying the present invention. As shown,transmitter 10 comprises three helically wrapped wire springs 12, 14,16.

As shown, the three springs are coaxial. Central spring 14 surrounds andengages the outer surface of inner spring 12, and itself is surroundedand engaged by the inner surface of outer spring 16. The outer diameterof device 10 is (for reasons discussed hereinafter with reference toFIG. 4) about 0.0128 in.; and this results in its inner diameter beingabout 0.0067 in.

Each of springs 12, 14, 16 is wrapped from a single strand of 304Vstainless steel, diamond drawn flat wire. In the illustrated embodimentall the wire strands are 0.00080 in. thick (measured radially of thespring) and 0.003 in. wide (measured generally axially of the spring),and each spring is wrapped at helix angle of about 7° with the sideedges of adjacent wire turns abutting each other. In transmitter 10,springs 12 and 16 are right hand wrapped (clockwise as viewed fromeither end), and spring 14 is left-hand wrapped (counterclockwise asviewed from either end). In practice, the coils of each spring are notprecisely axially aligned.

In actual practice, the coils of each spring are not wound preciselyflat to its longitudinal axis. Rather than being exactly coaxial to itsaxis and of precisely the same diameter, the coils may vary slightly indiameter and be slightly offset axially from each other. The result isthat the outer diameter of each spring is greater than the innerdiameter by an amount greater than twice the radial thickness of thewire strands from which the spring is wound.

For example, the outer diameter of each of springs 12, 14, 16 issomewhat more than 0.0016 in. greater than the inner diameter, (i.e., ismore than twice the 0.00080 in. thickness of the wire forming thespring). Typically, the coil diameter variation and coil-to-coilmisalignment is such that the difference between the overall inner andouter diameters of each spring in the device 10 is about 0.002 ratherthan 0.0016 in. Thus, in the assembled transmitter 10, the averagediameter of the generally cylindrical interface between inner spring 12and center spring 14 is about 0.0085 in., and the diameter of theinterface between center spring 14 and outer spring 16 is about 0.0105in. At each of the opposite ends 18, 19 of device 10, the ends of thethree springs are brazed or soldered together, preferably leaving centerbore 11 open, and the remaining portions of the springs engage but arerelatively movable against each other.

Inner spring 12 initially is wrapped so that, in a relaxed condition andunconfined by any other spring, its inner diameter is about 0.0076 in.and its outer diameter is about 0.0092-0.0096 in. According to thepreferred practice of the present invention, center layer spring 14initially is wrapped to the same size. The outer layer spring 16 iswrapped so that its unconfined and relaxed inner and outer diameters areabout 0.0089 in. and 0.0105-0.0109 in. respectively, i.e., are about thesame as that of the center spring 14 in the complete device.

Thus, it will be evident that when the springs are relaxed and out ofcontact with each other, the inner diameter of center spring 14 is lessthan the outer diameter of inner spring 12, while the center spring'souter diameter is greater than the inner diameter of outer spring 16.This coupled with the fact that the inner and outer diameters of theoverall device are, respectively, less and greater than the relaxedinner diameter of spring 12 and the relaxed outer diameter of spring 16,insures that, when the three springs are wrapped one around the other asshown in FIG. 1, there is an interference fit between center spring 14and inner and outer springs 12 and 16. The outer surface of inner spring12 presses tightly against the inner surface of center spring 14, sincethe relaxed outer diameter of inner spring 12 is greater than the innerdiameter of center spring 14 and the inner spring 12 must be reduced indiameter from its relaxed configuration to fit into the center spring.Similarly, the inner surface of outer spring 16 presses tightly againstthe outer surface of center spring 14, since the relaxed inner diameterof outer spring 16 is less than the outer diameter of center spring 14and the outer spring 16 must be expanded in diameter from its relaxedconfiguration to fit the center spring.

The exact relative inner and outer diameters of the spring may vary.Whatever the relative diameters, however, it is important that there bean interference fit between center spring 14 and the inner and outersprings 12, 16.

FIG. 2 illustrates a second three-layer device, generally designated 20,embodying the present invention. The device 20 of FIG. 2 is similar todevice 10 of FIG. 1 in that it comprises three coaxial helically-wrappedmulti-strand (as illustrated, double strand) springs, designated 22, 24,26 respectively. Center spring 24 surrounds inner spring 22 with thefacing circumferential surfaces of the two engaging (i.e., providing aninterference fit with) each other, while the outer surface of centerspring 24 is surrounded by, and forms an interference fit with the innersurface of outer spring 26. As in the device 10 of FIG. 1, the inner andouter springs 22, 26 are helically wrapped in one direction (right-handwrap, as shown) while the center spring 24 is wrapped in the otherdirection (as shown, a left-hand wrap). In all three springs, the helixangle is about the same, e.g., about 7°. The end portions 28, 29 of thesprings are brazed together.

In device 10, each of the springs was wrapped from a single strand offlat wire. The springs 22, 24, 26 of device 20 are wrapped from doublestrands of round wire. Each round wire strand has a diameter of about0.0015 in., and the strands are placed side-by-side and the springswrapped so that each double-strand turn, measured axially of the springis about 0.003 in. wide. When relaxed and unconfined, springs 22 and 24each have an inner diameter of about 0.010 in. and an outer diameter ofabout 0.013 in. The inner and outer diameter of outer springs 26, whenrelaxed and unconfined, are about 0.013 and 0.016, respectively. Theoverall inner and outer diameters of device 20, with the three springswrapped totally coaxially about each other, are about 0.009 in. and0.018 in., respectively. It will thus be noted that, in device 20, innerspring 22 is reduced about 0.001 in diameter from its relaxed state,while center spring 24 and outer spring 26 each are increased about0.002 in diameter.

The central conduit 21 through transmitter 20 is essentially watertight.Polymeric films are provided at the interface between springs 22 and 24and that between spring 24 and 26, typically by applying a thin layer ofliquid polymer during assembly and thereafter permitting it to cure.

Although the devices 10, 20 shown are rather short, e.g., the overalllength is only a few times the diameter, in actual use the devicestypically will have a length that is more than one hundred and often asmuch as a thousand times its diameter, e.g., a typical device will beabout a foot long and about 0.0120 in. to about 0.060 in. in diameter.

In many applications, it is desirable that if one end of the device isrotated a specific number of degrees the other end will rotate the sameamount, i.e., that there will be one-to-one rotation even under load,and even when the device is following a tortuous path.

In practice, perfect one-to-one rotation is impossible to achieve; underload there will always be some torsional deflection particularly as thedevice becomes very long relative to its diameter. The closestone-to-one rotation obtainable in the past, at least in relativelystraight devices, has been that provided by a solid rod. Theoreticalone-to-one transmission means that, regardless of the applied torque,there will be no relative rotational difference between the two ends ofa device. Since even a solid rod is not infinitely stiff (i.e., will nothave an infinitive modulus of elasticity), there will always be somerelative deflection. The straight line A in FIG. 3 illustrates therelative deflection with torque of a typical solid rod; with a stiffermaterial, the line would be more nearly vertical. The deflection versustorque characteristics of devices of the present invention is shown byline B. As will be seen, such torque transmitters closely approximatesolid rod characteristics; and unlike a solid rod the transmitter of thepresent invention will produce such linear and near one-to-one torsionalstiffness even when bent through tight curves. The interference fitbetween the three springs of devices 10, 20 ensures that, no matterwhich direction the device is rotated, there will be an immediateresponse at the far end.

In one method of manufacture of device 10, center spring 14 is firstplaced over and around spring 12 so that there is an interference fitbetween the two. In practice this is accomplished as follows. Both theinner and center springs are placed on a 0.0065 in. mandrel, i.e., on amandrel having an outer diameter that is less than the inner diameter ofinner spring 12 (typically by an amount about equal to or slightlygreater than the thickness of the wire forming the inner spring) inaxial alignment with the adjacent ends of the two springs spaced a shortdistance from each other. The mandrel is rotated about its axis in therotational direction such that, if the end of inner spring 12 farthestfrom central spring 14 is held fixed, against rotation, the inner spring12 can be wrapped down onto the mandrel if the other end rotates in thesame direction as the mandrel. The turns of spring 12 are thenprogressively (i.e., from the fixed and non-rotating end towards the endnearer spring 14) pressed against the mandrel (i.e., the spring is wipeddown onto the mandrel, starting at the fixed end. The inner spring thuswrapped down tight on the mandrel along its length, slightly increasingthe overall length of the inner spring 12 while reducing its outerdiameter of about 0.0081 in. (0.0065 in. plus twice the spring's 0.00080in. wire thickness). Then, with the mandrel still rotating in the samedirection, the adjacent ends of the tightly wrapped inner spring 12 andthe still essentially unrestrained center spring 14 are butted together,with the far end of center spring being held so that it will not rotate.

As should be evident, the frictional contact between the ends of innerspring 12 and center spring 14 tends (since the springs are wrapped inopposite directions) to open up center spring 14 (i.e., to increase itsinner and outer diameter) while keeping inner spring 12 wrapped down onthe mandrel; and the two springs are pushed axially towards each other,slipping center spring 14 over inner spring 12. The far ends of the twosprings are then released, permitting inner spring 12 to try to expand(open-up) in diameter while center spring 14 simultaneously tends tocontract (i.e., to close down), forming an interference fit between thetwo.

The same general procedure is used to fit outer spring 16 over theassembled inner and central spring unit. The just-assembledinner-central spring unit and the outer spring 16 are placed inspaced-apart axial alignment on a mandrel, typically having a diameterof about 0.0063 in., with their adjacent ends spaced slightly apart.

The direction of rotation of the mandrel is then reversed from that usedin assembling the inner-central spring unit, i.e., the mandrel isrotated such that, if the end of the inner-central spring unit farthestfrom outer spring 16 is held fixed against rotation, the central spring14 will tend to be wrapped down onto the inner spring 12 when theinner-central spring unit is pressed against (and thus tends to rotatein the same direction as) the mandrel. The central spring 14 is thenprogressively wiped down on the inner spring 12, starting at the fixedend. With the mandrel still rotating, the far end of the outer spring 16then is held so it will not rotate, and the outer spring is movedaxially so that its other end is butted against the inner-central springunit. The frictional contact between the ends tends to open up outerspring 16, while keeping central spring 14 wrapped down against theinner spring 12, and the outer spring 16 is slipped over theinner-central spring unit. When the springs are released, the outerspring 16 contracts, forming the desired interference fit between it andcentral spring 14.

Reference is now made to FIG. 4 which shows a guide wire assembly,generally designated 100, which can be steered along and into verynarrow blood vessels in cardiovascular surgical procedures. As shown,the guide wire assembly 100 may be used with balloon dilatationcatheters of the general type described in U.S. Pat. No. 4,195,637 andin aforementioned U.S. Pat. No. 4,545,390. Such catheters are well-knownin the art and are not part of the present invention.

An entire guide wire assembly of the type shown in FIG. 4 is often sixor more feet long, and guide wire 100 has an overall diameter of lessthan about 0.014 in. It will thus be appreciated that although FIG. 5 isgenerally to scale, diametrically, the scale along the length of thewire assembly is very different from that shown.

As illustrated, guide wire assembly 100 includes a distal tip portion102 about one inch long, an intermediate portion 104 about one foot longat the proximal end of tip portion 102, and a main guide wire portion106 extending some five feet from the proximal end of the intermediateportion 104. The solid main guide wire 108 includes an approximatelyconstant diameter portion about five feet long and 0.013 in. in diameterforming the main guide wire portion 108 of assembly 100 and a distalportion 110 of reduced diameter extending coaxially through intermediateportion 104 and terminating in a flat portion which is secured(typically by welding) at its distal end to the essentiallyhemispherical tip 112 of tip portion 102. It will be seen that thedistal portion 110 of guide wire 108 acts as a safety wire for the tipand intermediate portions of the guide wire assembly.

Tip portion 102 comprises a tapered spring 103 of helically wrappedplatinum wire (about 0.0015-0.0016 in. thick by 0.003 to 0.004 in. wide)having a diameter of about 0.013 in. at its proximal end (where it isbrazed to intermediate portion 104) and a diameter of 0.010 in. at itsdistal end (where it is welded to tip 112).

Intermediate portion 104 includes a torque transmitter 120 (essentiallyidentical to device 10 of FIG. 1) including a right hand inner spring122, a left hand central spring 124 and a right hand outer spring 126wrapped around each other so that there are interference fits betweenthe outside circumference of central spring 124 and the innercircumference of outer spring 126, and between the inner circumferenceof central spring 124 and the outer circumference of inner spring 122.As previously discussed, the adjacent spring layers are not connected toeach other except at their opposite ends where they are brazed, both toeach other and, respectively, to the tip and main guide wire portions102, 106. The braze areas, each of which have an overall length of about0.05 in., are indicated by shading and identified by the referencenumbers 130, 132.

A tantalum (or, alternatively, gold, tungsten or platinum) marker wirespring 140 is fitted over the reduced diameter portion 110 of guide wirewithin intermediate portion 104. The purpose of marker wire spring 140is to provide a good fluoroscope image to a physician using guide wireassembly 100, and there is only a loose fit between the marker wirespring 140 and guide wire portion 110 and between spring 140 and torquetransmitter 120.

A thin, e.g., 0.0005 in. thick, urethane film layer 142 is spraydeposited on the outer surface of main wire 108 from a point about twoinches from the wire's proximal end to and over the braze area 132 whereit is connected to intermediate portion 104. As will be evident, film142 increases the overall diameter of the guide wire assembly by about0.001. If, therefore, it is desirable that the overall diameter of theparticular assembly not exceed 0.014 in., the overall diameter of theguide wire 108 and of the torque transmitter 120 should not exceed 0.013in. or, to provide for manufacturing tolerances, 0.0128 in.

OTHER EMBODIMENTS

In such other embodiments, by way of example, the ends of the threesprings forming the torque transmitter may no be brazed together orotherwise fixed to each other, and the springs themselves may be what isknown in the field as an "open wind" in which the adjacent coils are notabutting.

Similarly one or two of the springs may be wound from single strand wirewhile the other springs are multiple (e.g., 2 to 6) strand windings; anddifferent spring also be made from different cross-section (e.g.,rectangular, square, round) wire.

Typically, the outer diameter of the overall torque transmitter will beless than about 0.060 in., and preferably less than about 0.030 in.; andthe wire from which the individual springs are wound will have athickness (measured radially of the wound spring) of less than 0.007in., and preferably in the range of 0.0005 to 0.003 in.

As used in the claims, the term "interference fit" between any twoadjacent spring layers of an assembled device means that the innerdiameter of the outer layer is less than the outer diameter of the innerlayer when the two layers are separated and no torque is being appliedto either. By way of example, there is in the device 10 of FIG. 1, thereis an "interference fit" between the outer spring 16 and the centerspring 14 because, when the outer spring 16 is separated from theinner-center spring unit (e.g., before the two are assembled) the innerdiameter of the outer opening is less than the outer diameter of theinner-center spring unit (and in the illustrated embodiment is less alsothan the outer diameter of the center spring 14 above). There also is an"interference fit" between the center spring 14 and the inner spring 12because, when the two springs are separated as before they areassembled, inner spring 12 has an outer diameter greater than the innerdiameter of center spring 14.

What is claimed is:
 1. A torque transmitter including three coaxialhelically wound springs, an inner spring, a center spring, and an outerspring, said springs having different inner and outer diameters andbeing positioned relative to each other such that said inner spring issurrounded by said center spring and said center spring is in turnsurrounded by said outer spring, and said inner and said outer springsbeing wrapped in one direction and said center spring being wrapped inthe opposite direction, said torque transmitter being characterized inthat:the inner generally circumferential surface of said center springforms an interference fit with the outer generally circumferentialsurface of said inner spring; and, the outer generally circumferentialsurface of said center spring forms an interference fit with the innergenerally circumferential surface of said outer spring.
 2. The torquetransmitter of claim 1 wherein end portions of said inner, center andouter springs are adjacent and are fixed against rotation relative toeach other and portions of said springs intermediate said end portionsare moveable relative to each other.
 3. The torque transmitter of claim1 wherein each of said springs is wrapped from generally flat wire. 4.The torque transmitter of claim 1 wherein at least one of said springsis wrapped from a multiple wire strand.
 5. The torque transmitter ofclaim 1 wherein the diameter of the generally circumferential outersurface of said outer spring is not more than about 0.060 in.
 6. Thetorque transmitter of claim 5 wherein said diameter is not more thanabout 0.030 in.
 7. The torque transmitter of claim 1 wherein the lengthof said transmitter is not less than about 100 times the diameter of thegenerally circumferential outer surface of said outer spring.
 8. Thetorque transmitter of claim 7 wherein said length is not less than about500 times said diameter.
 9. The torque transmitter of claim 1 whereineach of said springs is wrapped from wire having a thickness less thanabout 0.007 in., said thickness being measured radially of said torquetransmitter.
 10. The torque transmitter of claim 9 wherein saidthickness or diameter is in the range of 0.0005 to 0.003 in.
 11. Thetorque transmitter of claim 1 wherein the inner surface of said innercoil defines a generally cylindrical hollow cavity, the generallycylindrical surface of said outer spring has a diameter of not more thanabout 0.060 in., the length of said transmitter is not less than about100 times the diameter of said generally circumferential outer surfaceof said outer spring, and each of said springs is wrapped from wirehaving a diameter less than about 0.007 in.
 12. A medical guide wireassembly comprising:the torque transmitter of claim 1; and, a mainportion connected to said torque transmitter and generally axiallyaligned therewith, said main portion extending from a point proximal tothe end of said torque transmitter.